choices of the hi shelf eq frequency

hello guys,

I  am thinking of modding the hi shelf frequency of in my sony console. initially a broadcast console, its shelving is quite low (4,5khz i guess). it seems a very simple mod to do with just one cap to change ( C7 on the attached schematic).
I wanted to know what you thought was the most sensible choice for mixing music. I seems that the industry is locked with 8, 10 and 12 khz values.
also, how do you measure the hi shelve corner frequency? at its -3dB point ?  the shelving shapes are very smooth in general, with lo q.

any help will be  greatly appreciated

thanks

maxime

Check the attached simulated graph.
Generally, the turnover point is estimated at -3dB below max boost (or 3dB above max cut - since they are supposed to be symetrical).
So I would say 10-12 kHz (depending if the frequency response is limited to 20kHz or not).
It looks to me as a pretty standard choice of frequency.
OTOH, I understand very well that you wish to change it, since I've never been really satisfied with fixed-frequency
Different programs need different EQ.